Explanation: Our universe is a very dusty place. Dust
usually shows its presence by blocking out light emitted from
stars or nebula behind it, sometimes creating the illusion of a
horse's head or a sombrero hat.
But nobody really knows what a typical interstellar dust grain
looks like. By studying how dust absorbs, emits, and reflects
light, astronomers do know that interstellar dust is much different
than the cell and lint based dust found around a typical house.
Interstellar dust
grains are composed mostly
of carbon, silicon, and oxygen
and are usually less than about 1/1000 of a millimetre across.
Recent work indicates that most dust grains are not spherical.
The above picture shows the result of a fractal adhesion model
for dust grains involving random conglomerates of spherical compounds
of different properties, here artificially highlighted by different
colours.